1. Field of the Invention
The present invention relates to an apparatus for controlling the rotation speed of a motor, and more particularly, to an apparatus for controlling the rotation speed of a motor, which is capable of detecting the voltage and the current that are applied to the motor and controlling the rotation speed and torque.
2. Description of the Background Art
In general, information on the speed of the motor or flux information is essential to controlling instantaneous torque in an apparatus for controlling the speed of a motor, in particular, a synchronous reluctance motor (SYNRM). That is, a sensor of information on the rotation speed of the motor and a flux sensor such as a hall sensor, a resolver, and a pulse encoder are necessary. However, it is difficult to install the sensors and the sensors are sensitive to installation conditions. Therefore, the sensors are vulnerable to noise. Also, the sensors are expensive. According to a method for controlling a vector without a speed sensor, speed and torque are controlled without correcting speed errors with respect to change in the rotor resistance of the motor.
FIG. 1 shows the respective axes of a common SYNRM.
As shown in FIG. 1, in the stator side three-phase axes (U, V, and W axes), a phase difference between the U axis and the V axis is 120xc2x0. The phase difference between the V axis and the W axis is 120xc2x0. The phase difference between the W axis and the U axis is 120xc2x0. The xcex1 axis and the xcex2 axis are in a stationary coordinate system. The d axis and the q axis are synchronous axes. Also, the flux axis xcex8e of a rotor is an angle showing the phase difference between the U axis and the d axis. The conventional technology will now be described with reference to FIG. 2.
FIG. 2 is a block diagram showing the structure of the apparatus for controlling the rotation speed of the SYNRM according to the conventional technology.
As shown in FIG. 2, the apparatus for controlling the rotation speed of the SYNRM according to the conventional technology includes a first proportional integration (PI) controller 12 for receiving an error value obtained by comparing reference speed w*m with estimated speed w*m and outputting reference torque component current i*q for compensating for the error value, a second PI controller 15 for receiving an error value obtained by comparing reference magnetic flux component current i*d with real magnetic flux component current i*d and outputting the reference magnetic flux component current for compensating for the error value as a reference magnetic flux component voltage v*d, a third PI controller 16 for receiving an error value obtained by comparing the reference torque component current i*q with real torque component current i*q and outputting the reference torque component current for compensating for the error value as a reference torque component voltage v*q, a synchronous/stationary coordinate converter 17 for changing the reference magnetic flux component voltage v*d and the reference torque component voltage v*q from a synchronous coordinate system to a stationary coordinate system according to sine and cosine values sin xcex8 and cos xcex8 of the real magnetic flux angle xcex8 and outputting the reference voltages v*xcex1 and v*xcex2 in the stationary coordinate system, a three phase voltage generator 18 for converting the reference voltage v*xcex1 and v*xcex2 in the stationary coordinate system into three phase voltages vas, vbs, and vcs and outputting the three phase voltages vas, vbs, and vcs, an inverter 19 for applying the three phase voltages vas, vbs, and vcs generated by the three phase voltage generator 18 to the SYNRM, a rotor position detector 22 for detecting the position of the rotor of the SYNRM, a speed operator 24 for outputting the estimated speed wm from the position of the detected rotor, a signal generator 23 for generating the sine and cosine values sin xcex8 and cos xcex8 of the real magnetic flux angle xcex8 from the position of the detected rotor and outputting the sine and cosine values sin xcex8 and cos xcex8, a two phase current generator 20 for converting the three phase current detected when the SYNRM rotates into two phase current ixcex1 and ixcex2 and outputting the two phase current ixcex1 and ixcex2 and a stationary/synchronous coordinate converter 21 for converting the two phase current ixcex1 and ixcex2 into the stationary coordinate system and outputting the real torque component current iq and the real magnetic flux component current id. The operation of the apparatus for controlling the rotation speed of the SYNRM according to the conventional technology will now be described.
A first subtracter 11 obtains the error value by comparing reference speed w*e with the estimated speed we detected by the rotor position detector 22 during the rotation of the SYNRM and outputs the error value to the first PI controller 12.
A second subtracter 14 compares the reference magnetic flux component current i*d with the real magnetic flux component current id output from the stationary/synchronous coordinate converter 21 and outputs the obtained error value to the second PI controller 15 .
The second PI controller 15 outputs the reference magnetic flux component voltage v*d of the reference magnetic flux component current i*d for compensating for the error value obtained by the second subtracter 14 to the synchronous/stationary coordinate converter 17. At this time, a third subtracter 13 compares the reference torque component current i*q output from the first PI controller 12 with the real torque component current iq output from the stationary/synchronous coordinate converter 21.
The third PI controller 16 outputs the reference torque component voltage v*q of the reference torque component current i*q for compensating for the error value obtained by the third subtracter 13 to the synchronous/stationary coordinate converter 17. At this time, the reference magnetic flux component voltage v*d output from the second PI controller 15 is output to the synchronous/stationary coordinate converter 17.
The synchronous/stationary coordinate converter 17 receives the reference magnetic flux component voltage v*d, the reference torque component voltage v*q, and the sine and cosine values sin xcex8 and cos xcex8 of the real magnetic flux angle xcex8 output from the signal generator 23, generates the reference voltages v*xcex1 and v*xcex2 in the stationary coordinate system, and outputs the reference voltages v*60 and v*xcex2 in the stationary coordinate system to the three phase voltage generator 18.
The three phase voltage generator 18 converts the reference voltages v*xcex1 and v*xcex2 in the stationary coordinate system into the three phase voltages vas, vbs, and vcs in the stationary coordinate system and outputs the three phase voltages vas, vbbs, and vcs in the stationary coordinate system to the inverter 19.
The inverter 19 applies the three phase voltages vas, vbs, and vcs output from the three phase voltage generator 18 to the SYNRM. At this time, the rotor position detector 22 for detecting the position of the rotor of the SYNRM outputs the estimated speed wm to the first subtracter 11 through the speed operator 24.
The two phase current generator 20 receives the three phase current detected during the rotation of the SYNRM, generates the current ixcex1 and ixcex2 in the stationary coordinate system, and outputs the current ixcex1 and ixcex2 in the stationary coordinate system to the stationary/synchronous coordinate converter 21.
FIG. 3 is a vector diagram showing the voltage of the d axis of the to SYNRM and the voltage of the q axis of the SYNRM in a steady state.
As shown in FIG. 3, the equations of the voltages of the SYNRM are expressed by the d axis and the q axis that are the synchronous axes.                                           v            d                    =                                                    R                s                            ⁢                              i                d                                      +                                          L                d                            ⁢                                                ⅆ                                      i                    d                                                                    ⅆ                  t                                                      -                                          w                e                            ⁢                              L                q                            ⁢                              i                q                                                    ⁢                  
                ⁢                              v            q                    =                                                    R                s                            ⁢                              i                q                                      +                                          L                q                            ⁢                                                ⅆ                                      i                    q                                                                    ⅆ                  t                                                      -                                          w                e                            ⁢                              L                d                            ⁢                              i                d                                                                        [Equation  1]            
wherein, vd and vq refer to the d axis component and the q axis component of the voltage, respectively. id and iq refer to the d axis component and the q axis component of the current, respectively. Rs refers to the stator side resistance of the SYNRM. Ld and Lq refer to the inductance of the d axis and the inductance of the q axis, respectively.
When the SYNRM is in the steady state, the current differential term of the Equation 1 becomes xe2x80x980xe2x80x99 and is expressed by Equation 2. Equation 3 can express a torque equation.
xe2x80x83vd=Rsidxe2x88x92weLqiq 
vq=Rsiq+weLdidxe2x80x83xe2x80x83[Equation 2] 
wherein, weLd=Xd and weLq=Xq. Xd and Xq refer to the reactance of the d axis and the reactance of the q axis, respectively. Therefore, the Equation 3 that is the vector diagram can express the Equation 2. Also, the torque Equation is the Equation 3.                               T          e                =                              3            2                    ⁢                      P            2                    ⁢                      (                                                            L                  d                                -                                  L                  q                                                                              L                  d                                ⁢                                  L                  q                                                      )                    ⁢                                    (                                                V                  s                                                  w                  e                                            )                        2                    ⁢                      xe2x80x83                    ⁢                                    sin              ⁢                              xe2x80x83                            ⁢              2              ⁢              δ                        2                                              [Equation  3]            
wherein, Ld and Lq refer to the inductance of the d axis and the inductance of the q axis, respectively. xcex4 refers to the phase difference between a phase voltage Vs and the current of the q axis. P refers the number of poles of the rotor in the SYNRM.
Here, torque is inverse proportionate to vs/we and sin 2xcex4. Also, the torque is maximal when xcex4 is at an angle of 45 degrees when vs/we is fixed. However, current in a transient state includes a higher harmonics component and a direct current (DC) offset voltage. Accordingly, the differential term of the current does not become xe2x80x980xe2x80x99. Therefore, the speed and the position of the rotor of the SYNRM are detected in the state, where the higher harmonics component and the DC offset voltage are included.
However, in the apparatus for controlling the rotation speed of the SYNRM according to the conventional technology, the current detected by a torque ripple and switching dead time includes a fundamental wave and higher harmonics. Accordingly, the higher harmonics component is included in an induced voltage. As a result, a ripple occurs in the estimated and operated rotation speed. Therefore, it is not possible to precisely control the speed. The encoder and the hall sensor are used in the rotor position detector. It is difficult to install the encoder and the hall sensor.
Therefore, an object of the present invention is to provide an apparatus for controlling the rotation speed of a motor, which is capable of precisely controlling the rotation speed of the motor by removing a hall sensor and an encoder for estimating the speed and the position of a synchronous reluctance motor (SYNRM), to thus detect the speed and the position of the SYNRM in a place where the position of a rotor cannot be easily detected, such as the compressors of a refrigerator and an air conditioner and extracting only the induced voltage of a fundamental wave component, to thus estimate and to operate the rotation speed of the SYNRM.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for controlling the rotation speed of a motor, comprising a synchronous/stationary coordinate converter for comparing the reference speed of a motor with the estimated speed of the motor and outputting reference magnetic flux component current and reference torque component current for compensating for an error value according to the comparison result as the reference voltage of an xcex1 axis and the reference voltage of a xcex2 axis in a stationary coordinate system, a two phase current generator for receiving three phase current detected when the motor rotates and outputting the current of the xcex1 axis and the current of the xcex2 axis, and a speed/position estimation operator for estimating the position and the rotation speed of a rotor in the motor on the basis of the reference of the xcex1 axis, the reference voltage of the xcex2 axis, the current of the xcex1 axis, the current of the xcex2 axis, and reference speed and controlling the rotation speed and the torque of the motor.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.